How we made it: One Exchange Square

Sitting above and adjacent to Liverpool Street Station, facing Bishopsgate and centre of the Exchange Square Complex, One Exchange Square is the refurbishment and extension of a 1980s office building.

Navigating complex Network Rail infrastructure below and retaining 94% of the existing structure, the redevelopment provides an additional 7710 sqm of office and terrace space without requiring any new foundations.

• Location: City of London
• Client: PNB, La Salle
• Development Manager: M3 Consulting
• Architect: Fletcher Priest Architects
• Size: (GIA) 58,955m²
• Stage: On site
• Time Frame: 2020-2026

Navigating Network Rail infrastructure

The building’s location above the platforms and tracks of Liverpool Street Station meant that no new foundations could be installed, nor any strengthening to the lowest storey of the building, and access for investigations was very limited.

Through a carefully managed process with Network Rail, we justified the capacity of the existing foundations based on site investigations within the station. BIM models were based initially on archive information and localised structural investigations, followed by point cloud surveys of the stripped-out building.

Creating additional floorspace

We justified an additional 13% internal floor area within the capacities of the existing substructure, achieved in three ways: lightweight vertical extensions, partial atria infill and a part-cantilevered, part-hung extension on the west side of the building.

Infilling the atria of the existing building created 1553 m² of additional floor space. This involved extending the floorplates and rationalising the large opening to a single bay of each floor.

Managing additional loads

The new extensions produced a load increase of up to 40% on the structure. We justified this through careful back analysis of the original structure, localised strengthening and specialist geotechnical input as part of the foundation re-use strategy.

Once complete, much of the structure will be left exposed and visible. This maximises the already generous heights to the underside of the slab and expresses the industrial aesthetic of the surrounding area.

Designed as an exoskeleton

The new west extension is designed to hang off the existing building as an exoskeleton. Its structure is supported on two primary hangers which transfer the load back via horizontal bracing beams to the retained, strengthened cores.

The perimeter columns and projecting stud members are beyond the cladding line and have been designed for the full range of thermal load effects that the building will see during its lifetime.

By retaining 94% of the existing structure, One Exchange Square achieves a carbon saving of around 12,000 tonnes compared to an equivalent new build office.

Once completed, the overall structural embodied carbon of the building will be 55 kgCO2e/m2; less than a third of that of a typical lower carbon new build.

Boasting an additional 20% area overall, including new roof terraces and external gardens, One Exchange Square is set to complete in early 2026 and is targeting BREEAM Outstanding, WELL Platinum and a NABERS UK DfP 5-star Rating.